In order to subsequently handle partially consolidated extruded tubes previously made by powder metallurgical processes, it has been determined that the tubular product (or preform) must be further consolidated to near theoretical density before the tube may be conventionally worked (drawn, extruded, forged, swaged, etc.). Any subsequent thermomechanical processing, such as sintering and final consolidation to higher final density, of the preform tube must be accomplished in a protective atmosphere.
Experimental work has demonstrated the need to hot work (by compression) the tubular preform while it is at the sintering temperature and under a reducing, inert, or vacuum atmosphere. This means that the furnace, hot working device and material movement equipment must all be under atmosphere. Experiments with nickel-base alloy powders, such as INCOLOY.RTM. alloy 825, have shown that such powders do not appreciably shrink during sintering. (INCOLOY is a trademark of the INCO family of companies). Moreover it is desirable that the sintering cycle be of short duration in order to conserve energy.